When is the turning gear engaged when taking a turbine off-line?

• A. Immediately
• B. When the turbine has reached full load
• C. When the turbine coasts to a stop
• D. Prior to starting the turbine

Answer: (C)

The turning gear is engaged when a turbine coasts to a stop to help maintain the integrity of the machine during the shutdown process. This mechanism is essential for preventing thermal distortion of the turbine components and ensuring that all parts of the turbine come to a uniform temperature. By engaging the turning gear as the turbine is slowing down, it allows for slow and controlled rotation, minimizing the risk of damage due to any excessive thermal stresses.

Engaging the turning gear immediately or when the turbine is at full load would not be appropriate, as it could interfere with normal operational procedures and dramatic changes in operational speeds can lead to mechanical wear. Additionally, engaging the turning gear prior to starting is not necessary as the turbine needs to be at rest or coasting down to benefit from the turning gear's function in maintaining proper alignment and cooling rates.